The invention relates to optical data storage. More specifically, the invention relates to an optical disk having timing and address information embossed in a wobbled groove.
“Read/write” optical disks include optical disks that allow data to be written only once and optical disks that allow data to be written many times. A DVD+RW disk is a type of read/write disk that allows data to be written many times.
When writing data to a read/write disk, it is desirable not to create a frequency or phase discontinuity between the data being written (“new” data) and data previously written (“old” data). A read/write drive might not be able to tolerate such discontinuities during readback of the old data and the new data. During readback, the discontinuities can cause problems for read clocks and data recovery circuitry. Consequently, the discontinuities can render portions of the read/write disk effectively unreadable by the read/write drive.
Certain types of drives overcome this problem by the use of “edit gaps” (also known as “splice areas” and “buffer zones”). Edit gaps are spaces that separate data blocks. An edit gap provides a margin of error so that old data is not overwritten by new adjacent data. However, the use of edit gaps has its drawbacks. Storage capacity of the read/write disk is reduced because data is not stored in the edit gaps.
Other types of drives overcome the phase/frequency discontinuity problem by performing bit-accurate or linkless editing, whereby new blocks of data are written with negligible frequency or phase discontinuity with respect to adjacent blocks of old data. This bit-accurate editing is accomplished by exploiting accurate timing information embossed in a high frequency wobbled groove in the read/write disk. The bit-accurate editing eliminates the need for edit gaps.
When writing new data to a read/write disk, a bit-accurate read/write drive modulates the wobbled shape of the groove to generate a raw wobble signal. A wobble clock may be generated by a phase locked loop (PLL) that is locked to a harmonic of the raw wobble signal. The wobble clock provides an extremely accurate time reference, which is insensitive to misalignments. Edges of data marks can be aligned with edges of the wobble clock with a high degree of accuracy.